1. Field of the Invention
This invention relates to a portable electronic device and, more particularly, to a portable electronic device with two casings.
2. Description of the Related Art
With development of information, network, and communication industries, in need of fast, distinct, and stable communication quality, a receiving antenna of a communication product such as a mobile phone is mostly an exposed antenna at first, starting with a five-sectioned antenna and then going through a retractable antenna, a long soft antenna, a nickel titanium retractable antenna, and a short hard antenna. In recent years, with light, slim, short, and small needs of users for the communication product, hidden antennas are widely used.
When a hidden antenna is used in a wireless communication device, a size and position of the antenna and materials of surrounding elements thereof need to be considered. A mobile phone with a replaceable casing in the market is taken for example. A wireless communication module with a hidden antenna is always used to cooperate with casings with different shapes or colors thus to satisfy new and changeable needs of users. However, as far as an antenna with a better design and covering multiple frequencies (such as GSM900/DCS/PCS/WCDMA) is considered, a medium (that is, the casing) disposed above the antenna usually causes a resonance frequency of the antenna to deviate to the low frequency. In addition, if the medium is closer to the antenna and the thickness is greater, the deviation of the resonance frequency of the antenna may be more serious. Relatively, with the deviation of the resonance frequency, the antenna fails to cover a predetermined frequency band, and the radiation characteristic of the antenna may also change.
At present, the frequency deviation of the antenna is usually improved by increasing the operation bandwidth of the antenna or using a frequency tuning antenna. However, to increase the bandwidth of the antenna, usually the antenna with a greater size is needed, which limits microminiaturization development of the wireless communication device. In addition, the frequency tuning antenna needs to use extra circuits to reconfigure the antenna to change the resonance frequency of the antenna. The resonance frequency of the antenna can be changed by changing reactance between a radiation surface and a ground surface of the antenna or switching a conduction state of a tuning stub of the antenna.
However, no matter what kind of modes, the frequency tuning antenna usually needs to use separate elements such as direct-current wires, radio-frequency switches, and variable capacity to achieve the structure reconfiguration, and the electronic elements and the direct-current wires may reduce the radiation characteristic of the adjacent antenna. Further, to achieve the structure reconfiguration of the antenna, the frequency tuning antenna is more complex than the general antenna in design.